Assessment of occupational exposures is a crucial factor in evaluating dose-response relationships and most human population-based studies conducted by the Branch have an extensive exposure assessment component. Major assessment efforts in cohort studies have involved exposures to pesticides, benzene, polycyclic aromatic hydrocarbons, and diesel exhaust fumes, and to a broad range of exposures in a cohort study of women in Shanghai and shipyard workers. Cross-sectional studies are being conducted to study the effect of benzene, diesel exhaust, trichloroethylene, and atrazine on genotoxic, immune, and hormonal parameters. In the case-control design, jobs have been evaluated for a wide variety of exposures, including solvents (including chlorinated hydrocarbons, aromatic, and other solvents), metals (arsenic, chromium, cadmium, lead), electromagnetic fields, polychlorinated biphenyls, dusts (wood dust and other types) , asbestos, formaldehyde, physical activity, nitrosoamines, polycyclic aromatic hydrocarbons, gasoline and diesel exhausts, aromatic amines, and pesticides. These exposures have been evaluated in studies of cancer of the bladder, brain, breast, kidney, lung, larynx, and the lymphatic and hemtopoietic system, and of childhood brain cancer, germ cell tumor cancer, and leukemia Ewings sarcoma and possible associations with parental occupations. Methodologic studies are also conducted to improve exposure assessment techniques and to understand exposure patterns, such as peak exposures. A study has been conducted in Shanghai to evaluate assessments made from detailed occupational questionnaires with air measurements. A report describing the exposure assessment procedures for evaluating EMF exposures in a brain cancer case-control study has been published. Reports describing the occurrences of pesticides, polychlorinated biphenyls, chlorinated and aromatic solvents, wood dust, lead, cadmium, and nitrosoamines are being prepared. Detailed questionnaires have been developed for several case-control studies: a kidney cancer study in the US, a bladder cancer study in New England, a NHL study in the US, and a bladder cancer study in Spain, and the recently launced AsiaLymph Study. A comparison of assessments to pesticides has been compared to pesticide metabolites in the urine. Important determinants of exposure to 2,4-D has been evaluated using urinary levels. Historical benzene and lead exposure estimates have been developed using a novel framework that combines job-exposure matrices with databases of inspection measurements to predict exposure for a population-based cohort of women in Shanghai. Data mining models have been used to extract decision rules from questionnaire responses and previously assessed exposure metrics for occupational diesel exhaust exposure so that the decision rules can be used in subsequent studies. The same data mining approaches will be used for other agents. An algorithm-based approach that efficiently links expert-based exposure decisions to participants responses to exposure-oriented modules was developed to estimate occupational diesel exhaust exposure and was compared to estimates from an expert review of each individual job. Exposure estimates for lead and cadmium exposure are being developed for the kidney cancer study. A study evaluating gender differences in work tasks and exposure within men and women reporting the same job title is underway.